The ITU list of modulation designations and codes is used by many organisations including the FCC to describe a radio transmission format or modulation type in a succinct format.

The ITU, International Telecommunications Union uses an agreed set of codes or designations to easily and succinctly describe a format and modulation for a radio transmission.

The designators are used by many licencing authorities around the globe including the FCC in the USA. Accordingly they are often referred to as FCC emission designators.

These codes or emission designations are used in a variety of different areas including defining what types of transmission may be used in different portions of the radio spectrum in the ITU list agreed at the World Radio Conferences as well as defining radio transmission formats in licences and other documents.

The ITU radio emission designations define many aspects of the signal: the type of modulation, bandwidth and the type of information being carried. As such the type of radio emission, or transmission is defined in an exact manner. It should be noted that the designations describe the emission and not the transmitter or the system that is used.

The ITU designator system was agreed at the 1979 World Administrative Radio Conference, WARC 79, and superseded a previous system which has now completely fallen out of use. It is worth noting that the WARC was the old name for the conferences, they are now just called World Radio Conferences, WRC.

Radio emission types designators format

The ITU designations for the different types of radio emissions follows a standard format. This enables anyone using the system to quickly identify the parameters of the particular transmission. Although not all elements of the system may be used every time, it has been developed so that there is no ambiguity whatever part of the system for describing the types of radio emission is used.

The system has the following format:

BBBB 123 45

Where:
BBBB are characters that define the bandwidth
Character "1" is a letter indicating the type of modulation
Character "2" is a digit that indicates the type of modulating signal
Character "3" is a letter indicating the type of information being transmitted
Character "4" is an optional letter indicating the practical details of the transmitted information
Character "5" is an optional letter indicating details about any multiplexing, if used.

Tables for the different characters 1 to 5 are given below.

Bandwidth designator list

The bandwidth designator has the format of three digits that express the significant figures, and a letter used for the decimal point.

Independent sideband, i.e. two sidebands present, each carrying different information

C

Vestigial sideband

D

Combination of AM and FM or PM, either simultaneously or in a pre-established sequence

F

Frequency modulation, FM

G

Phase modulation, PM

H

Single sideband full carrier

J

Single sideband suppressed carrier, SSBSC

K

Pulse amplitude modulation, PAM

L

Pulse width modulation, PWM

M

Pulse position modulation, PPM

N

Un-modulated carrier

P

Series of pulses without modulation

Q

Sequence of pulses, phase or frequency modulation within each pulse

R

Single sideband with reduced or variable level carrier

V

Combination of pulse modulation methods

W

Combination of any of above

X

cases not covered by the above definitions

It is worth noting that frequency modulation and phase modulation may also be referred to by the generic term: "angle modulation."

Character 2 - type of modulating signal

This character of the ITU designations for radio emissions details the characteristics of the modulating signal. It provides information including whether the modulation is analogue or digital and whether there is one channel of information or more being carried.

List of Emission Designators for Character 2

Letterindicator

Details

0

No modulating signal

1

One channel containing digital information without the use of modulating sub-carriers (excludes time division multiplex)

2

One channel containing digital information with the use of a modulating sub-carrier (excludes time division multiplex)

3

One channel containing analogue information

7

More than one channel containing digital information

8

More than one channel containing analogue information

9

Combination of analogue and digital channels

X

cases not covered by the above

Character 3 - type of transmitted information

This character in the ITU designation of radio emissions details the type of information being carried. It provides some insight into the use and the way in which the information may be decoded.

Four-condition code in which each condition represents a signal element (or one or more bits)

E

Multi-condition code in which each condition represents a signal element (of one or more bits)

F

Multi condition code - one character represented by one or more conditions

G

Monophonic broadcast quality sound

H

Stereophonic or quadraphonic broadcast quality sound

J

Commercial, non-broadcast, quality sound (but excluding K & L below)

K

Sound of commercial quality with the use of frequency inversion and/or band-splitting employed

L

Sound of commercial quality with independent FM signals to control the level of the demodulated signal, e.g. pilot tones used to control demodulation process

M

Monochrome images or video

N

Full colour images or video

W

Combination of the above

X

Cases not covered by the above descriptions

Character 5 - details of multiplexing

Increasingly radio channels are used to carry more than one stream of information, or they may be required to share the channel with other users or streams of information. This character in the ITU designation of radio transmissions provides information about any multiplexing.

The list of radio emission designators is widely used, especially within licences and other documentation. The ITU emission designators provide an easy method of accurately defining the form of transmission that is being used.